Dear Bill and All,
I have had another thought on finding the average pressure at (or
near) the surface of the Earth. As you will see, I am trying to derive
the average by calculation. Our previous correspondence is below. I
would appreciate any thoughts you might have on this way of proceeding
and particularly on my calculations.
National Center for Atmospheric Research
According to the National Center for Atmospheric Research, "The total
mean mass of the atmosphere is 5.1480 x 1018 kg with an annual range
due to water vapor of 1.2 or 1.5 x 10^15 kg depending on whether
surface pressure or water vapor data are used; somewhat smaller than
the previous estimate. The mean mass of water vapor is estimated as
1.27 x 10^16 kg and the dry air mass as 5.1352 ±0.0003 x 10^18 kg."
Calculation
Mass of Earth's
atmosphere
= 5.1480 x 10^18 kilograms
Weight of atmosphere = mg = m x 9.80665 m/
s2 = 50.48463 x 10^18 newtons
Surface area of Earth = 4 π r2 = 4 x π x (6.378 137 x10^6)^2
m = 511.207 8 x 10^12 square metres
Average pressure at sea level (Force ÷
area) = 98.755 58 x 10^3 pascals =
98.756 kPa
Irrelevant information about the atmosphere and the Earth
The average mass of the atmosphere is about 5 teratonnes (= 5.1480 x
10^18 kilograms).
The average mass of the Earth is about 6 zettatonnes (= 5.9742 × 10^24
kilograms).
The proportion of the whole Earth to its atmosphere is roughly 1 000
000 to 1, that is if the atmosphere was valued at 1 cent then the
Earth would be valued at $10 000.00.
Cheers,
Pat Naughtin
Author of the ebook, Metrication Leaders Guide, that you can obtain
from http://metricationmatters.com/MetricationLeadersGuideInfo.html
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that they
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On 2009/12/05, at 08:51 , Bill Hooper wrote:
On Dec 4 , at 11:38 AM, Pierre Abbat wrote (in response to my
earlier note):
(I wrote) Normal or
average atmospheric pressure is about 101.3 kPa. (There may be
different
standards for identifying "normal" or "average" air pressure.)
(Pierre replied)
101.325 kPa, to be exact, is the standard.
The value of 101.325 kPa is the exact value (the "standard")
specified by CGPM for the standard atmospheric pressure, as Pierre
correctly points out. That value is as close to a universal value as
is possible.
In addition, however, there are other circumstances where different
standards are used. Here are two I've encountered (from Wikipedia):
... International Union of Pure and Applied Chemistry (IUPAC)
recommended that for the purposes of specifying the properties of
substances, “the standard pressure” should be defined as
precisely 100 kPa ... rather than the 101.325 kPa value of “one
standard atmosphere”. ... For natural gas, the petroleum industry
uses a standard temperature of 15.6 °C (60.1 °F), pressure 101.56
kPa (14.730 psi). (air pressure)
The CGPM standard is probably more precise than is reasonable for
many uses, such as reporting air pressure in weather reports. For
such measurements, a rounder value of 101.3 kPa or even 101 kPa
might be suitable as a state "normal" or "average".
Certainly, atmospheric pressure is affected by altitude and other
factors. For specific locations or specific special conditions, the
CGPM standard atmosphere may not be too close to the actual average
of the ambient pressure.
This is not meant to be argumentative. I recognize the value of
101.325 kPa as the best value to use for most technical purposes. I
just felt it was necessary to indicate in my note that there are
different possible averages or normal values that might be used.
Regards,
Bill Hooper
==============================
If you have not already done so,
please note my new email address:
billhoope...@gmail.com
(Old address will still work OK temporarily.)
